expand - convert tabs to spaces
expand [-t tablist] [file...]
The expand utility shall write files or the standard input to the standard output with <tab> characters replaced with one or more <space> characters needed to pad to the next tab stop. Any <backspace> characters shall be copied to the output and cause the column position count for tab stop calculations to be decremented; the column position count shall not be decremented below zero.
The expand utility shall conform to XBD Utility Syntax Guidelines.
The following option shall be supported:
- -t tablist
- Specify the tab stops. The application shall ensure that the argument tablist consists of either a single positive decimal integer or a list of tabstops. If a single number is given, tabs shall be set that number of column positions apart instead of the default 8.
If a list of tabstops is given, the application shall ensure that it consists of a list of two or more positive decimal integers, separated by <blank> or <comma> characters, in ascending order. The <tab> characters shall be set at those specific column positions. Each tab stop N shall be an integer value greater than zero, and the list is in strictly ascending order. This is taken to mean that, from the start of a line of output, tabbing to position N shall cause the next character output to be in the (N+1)th column position on that line.
In the event of expand having to process a <tab> at a position beyond the last of those specified in a multiple tab-stop list, the <tab> shall be replaced by a single <space> in the output.
The following operand shall be supported:
- The pathname of a text file to be used as input.
See the INPUT FILES section.
Input files shall be text files.
The following environment variables shall affect the execution of expand:
- Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files), the processing of <tab> and <space> characters, and for the determination of the width in column positions each character would occupy on an output device.
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.
The standard output shall be equivalent to the input files with <tab> characters converted into the appropriate number of <space> characters.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- Successful completion
- An error occurred.
The expand utility shall terminate with an error message and non-zero exit status upon encountering difficulties accessing one of the file operands.
The expand utility is useful for preprocessing text files (before sorting, looking at specific columns, and so on) that contain <tab> characters.
See XBD Column Position.
The tablist option-argument consists of integers in ascending order. Utility Syntax Guideline 8 mandates that expand shall accept the integers (within the single argument) separated using either <comma> or <blank> characters.
Earlier versions of this standard allowed the following form in the SYNOPSIS:expand [-tabstop][-tab1,tab2,...,tabn][file ...]
This form is no longer specified by POSIX.1-2017 but may be present in some implementations.
XBD Column Position, Environment Variables, Utility Syntax Guidelines
First released in Issue 4.
This utility is marked as part of the User Portability Utilities option.
The APPLICATION USAGE section is added.
The obsolescent SYNOPSIS is removed.
The LC_CTYPE environment variable description is updated to align with the IEEE P1003.2b draft standard.
The normative text is reworded to avoid use of the term "must" for application requirements.
Austin Group Interpretation 1003.1-2001 #027 is applied.
SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.
The expand utility is moved from the User Portability Utilities option to the Base. User Portability Utilities is now an option for interactive utilities.
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